The principal prior art in all of these areas are mechanical feeler gages and flush pin gages which have been historically used for these measurements. Lately, the error prone manual recording of data from such feelers has been replaced by a mechanical type of caliper containing an electronic sensor such as an LVDT which is capable of measuring either gap or flushness at any one time and communicating this to a data acquisition module.
While a great improvement in eliminating errors in recording data, these present mechanical feelers, such as the one sold under the name "Datamyte" still suffer several disadvantages.
1. They require two steps to take the data to obtain both gap and flushness, the first step being to insert feeler in the gap, and the second to turn the unit over and press it against the panel to read flushness.
2. The gap width must be at least a minimum of several millimeters in order that one can stick a relative cumbersome mechanical feeler into the gap. This requires expensive modification of large numbers of existing fixtures or setting up of measuring problems in an artificial manner to achieve such larger gaps in many cases. In addition there are some small gaps as on aircraft that are simply unmeasurable in this fashion.
3. The mechanical contacts are subject to wear and breakage, both of the contact unit itself and of the object contacted. This means that it is difficult to use such units on plastic or on painted surfaces where the paint can be scraped off by the action of the feeler.
4. Due to some of the mechanical aspects the measurements are generally less repeatable than those of the present invention when used in a hand-held manner.
5. Because of the requirement for mechanical insertion and contact into a narrow gap, such units are useless for automatic robotic inspection.